The long range aim of our project is to characterize the messenger RNA, in particular the specific messengers for immunoglobulin, in mouse myeloma cells. No mammalian messenger RNA (mRNA) has been well characterized chemically and the immunoglobulin mRNAs are of particular biological interest. Mouse myeloma cells have been selected for this study because they are monoclonal cell lines which grow rapidly in culture (essential for effective radioactive labelling) and synthesize significant amounts of a single species of immunoglobulin. Our major goals at present are to isolate highly purified immunoglobulin messengers, to study the translation of the messengers in cell-free systems, and eventually to determine parts of their nucleotide sequence. The structural information that we would like to acquire about the immunoglobulin messengers is the exact size of the messengers, the sequence and location of non-coding regions (including poly-A sequences), the presence of secondary structure, the end groups of the RNAs and the nature of any special modified bases which may be present. We plan to relate this work to similar studies on total mRNA in these cells. We believe that this kind of precise structural information is an essential prerequisite for understanding the ways in which mRNA functions.